ee_extract: Extract values from EE Images or ImageCollections objects
In ryali93/rgee: R bindings for calling the Earth Engine API

Description Usage Arguments Details Value Examples

Extract values from a ee$Image or ImageCollection at the locations of a geometry object. You can use ee$Geometry$*, ee$Feature, ee$FeatureCollection and sf objects. This function try to mimics how extract currently works.

1	ee_extract(x, y, fun = ee$Reducer$mean(), scale = 1000, sf = FALSE, ...)

`x`	ee$Image or ee$ImageCollection with a single band.
`y`	ee$Geometry$*, ee$Feature, ee$FeatureCollection or sf objects.
`fun`	ee$Reducer object. Function to summarize the values. The function should take a single numeric vector as argument and return a single value. See details.
`scale`	A nominal scale in meters of the Image projection to work in. By default 1000.
`sf`	Logical. Should the extracted values be added to the data.frame of the sf object y? This only applies if y is a sf object.
`...`	reduceRegions additional parameters. See ee_help(ee$Image()$reduceRegions) for more details.

In Google Earth Engine the reducer functions that return one value are:

allNonZero: Returns a Reducer that returns 1 if all of its inputs are non-zero, 0 otherwise.
anyNonZero: Returns a Reducer that returns 1 if any of its inputs are non-zero, 0 otherwise.
bitwiseAnd: Returns a Reducer that computes the bitwise-and summation of its inputs.
bitwiseOr: Returns a Reducer that computes the bitwise-or summation of its inputs.
count: Returns a Reducer that computes the number of non-null inputs.
first: Returns a Reducer that returns the first of its inputs.
firstNonNull: Returns a Reducer that returns the first of its non-null inputs.
kurtosis: Returns a Reducer that Computes the kurtosis of its inputs.
last: Returns a Reducer that returns the last of its inputs.
lastNonNull: Returns a Reducer that returns the last of its non-null inputs.
max: Creates a reducer that outputs the maximum value of its (first) input. If numInputs is greater than one, also outputs the corresponding values of the additional inputs.
mean: Returns a Reducer that computes the (weighted) arithmetic mean of its inputs.
median: Create a reducer that will compute the median of the inputs. For small numbers of inputs (up to maxRaw) the median will be computed directly; for larger numbers of inputs the median will be derived from a histogram.
min: Creates a reducer that outputs the minimum value of its (first) input. If numInputs is greater than one, also outputs additional inputs.
mode: Create a reducer that will compute the mode of the inputs. For small numbers of inputs (up to maxRaw) the mode will be computed directly; for larger numbers of inputs the mode will be derived from a histogram.
product: Returns a Reducer that computes the product of its inputs.
sampleStdDev: Returns a Reducer that computes the sample standard deviation of its inputs.
sampleVariance: Returns a Reducer that computes the sample variance of its inputs.
stdDev: Returns a Reducer that computes the standard deviation of its inputs.
sum: Returns a Reducer that computes the (weighted) sum of its inputs.
variance: Returns a Reducer that computes the variance of its inputs.

A data.frame or a sf object depending on the sf argument. The columns with the extracted values will get their column name from the image metadata property RGEE_NAME. If is not defined ee_extract will use the band name for ee$Images and the system:index property for ee$ImageCollections.

## Not run: 
library(rgee)
library(sf)

ee_reattach() # reattach ee as a reserved word
ee_Initialize()

# Define a Image or ImageCollection: Terraclimate
terraclimate <- ee$ImageCollection("IDAHO_EPSCOR/TERRACLIMATE")$
  filterDate("2001-01-01", "2002-01-01")$
  map(function(x){
    date <- ee$Date(x$get("system:time_start"))$format('YYYY_MM_dd')
    name <- ee$String$cat("Terraclimate_pp_", date)
    x$select("pr")$set("RGEE_NAME", name)
  })

# Define a geometry
nc <- st_read(
  dsn = system.file("shape/nc.shp", package = "sf"),
  stringsAsFactors = FALSE,
  quiet = TRUE
)

# Extract values
ee_nc_rain <- ee_extract(
  x = terraclimate,
  y = nc,
  scale = 250,
  fun = ee$Reducer$mean(),
  sf = TRUE
)

# Spatial plot
plot(
  ee_nc_rain["Terraclimate_pp_2001_01_01"],
  main = "2001 Jan Precipitation - Terraclimate",
  reset = FALSE
)

## End(Not run)